In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date:    (i) part of common general knowledge; or    (ii) known to be relevant to an attempt to solve any problem with which this specification is concerned.
Most surfcraft (including surfboards) have one or more fins located on an underside of the surfcraft for controlling the direction and facilitating turning of the surfcraft. Some surfcraft have the fins integrally formed on the surfcraft. In recent times however it has become more common for surfcraft to incorporate fin systems which include removable fins. Such systems have numerous benefits including enabling the fins to be removed whilst travelling, allowing damaged fins to be easily replaced and enabling fins of different shapes or styles to be selectively used. Such fin systems typically include a fin plug embedded into the underside of the surfcraft. This fin plug generally has at least one cavity adapted to receive a base portion (or a base element) of a surfcraft fin. The surfcraft fin is attached to the surfcraft by securing the base portion (or base element) of the fin into the cavity (or cavities) of the fin plug. There are numerous known fin systems which adopt this arrangement.
One such known fin system is described in U.S. Pat. No. 5,464,359 in the name of Fin Control Systems Pty Ltd. This system includes fins having 2 projecting base elements (or tabs) and, for each fin, two fin plugs installed in the underside of the surfcraft. Each of the fin plugs has a cavity for receiving one of the base elements. Each fin plug also includes means for securing the base element into the cavity.
Other known fin systems comprise a single fin plug, with a single cavity, for each fin. Typically, such a fin system has quite a large tin plug with an elongated fin cavity for receiving the base element of the fin. The fin plug of such systems also typically includes an upper flat portion having an opening from which the fin cavity extends inwardly and a flange section extending laterally about the opening. This flange section has a particular width. Extending downwardly from an underside of the flat upper portion is a body portion which surrounds the fin cavity. The shape of such a fin plug generally requires two cavities to be routed into the underside of the surfcraft in a two step process. Firstly, a relatively wide, shallow cavity needs to be formed, the dimensions of which substantially correspond to the shape of the flange section. The depth of this first cavity will substantially correspond with the width of the flange section. Secondly, a narrow, deeper cavity needs to be formed in the first mentioned cavity, which is adapted to receive the body portion of the fin plug. As most surfcraft are designed to accommodate three fins, having to adopt this two step process for forming each fin plug cavity in the surfcraft substantially slows down the installation process.
These large fin plugs with elongated cavities can also cause other problems in the surfcraft into which they are installed. For instance, when one of these large fin plugs is used for the side fins of a surfboard, a rear section of the fin plug is necessarily positioned very close to the side rail of the surfboard. This makes installation of the fin plug more difficult and may cause the surfboard maker to compromise the positioning of the fin plug. Also, the size and length of such a fin plug causes there to be a very significant flex differential between the fin plug and the surfboard blank into which the plug is installed. This creates a defined weak point near the tail of the surfboard. Another problem caused by the length of such a fin plug is that the ‘shapers dot’ (which defines the location of the trailing edge of a fin) on the surfboard blank is removed due to the size of the fin plug cavity routed into the blank. This can give rise to doubts as to whether the fin plug has been correctly positioned in the surfboard.
A further problem with known fin plugs is that they are surrounded by the relatively low density foam of which the surfcraft is formed. Such foam does not generally provide sufficient strength to support the loads placed upon the fin plug, due to forces applied to the attached fin, without some deformation or weakening of the surrounding foam over time. Such deformation or weakening of the foam can cause the fin plug to sink into the foam or to shift out of alignment, with consequential reduction in performance of the attached fin. This can also cause the fibreglass skin, in the vicinity of the fin plug, to crack or shatter. Also, when the fin plug sinks into the foam body, it can cause the top surface of the plug to de-laminate from the adjoining fiberglass layer.
The present invention is directed towards ameliorating at least some of the above described problems associated with prior art fin plugs and, consequently, the methods of installing these. In particular, the present invention is directed towards providing a fin plug assembly which is relatively lightweight and strong and which is easier to install than many known fin plugs.